So if that is indeed the case (which I figured it would be but wanted to make sure) then would you choose to discard one copy if, as mentioned in the second scenario, a second copy of your unique hero (David) was released to your territory via Raiders' Camp?
No, you couldn't release David to a territory where one already is. All cards for a character already controlled by a player are protected from abilities that would put them under that player's control.
So, if you only had a captured David in your Raider's Camp, and it is owned by your opponent, and they had another David already in territory (playing a different version, for example), then you could not release David from Raider's Camp "instead" of surrendering a soul; you would have to surrender a soul because you have no targets that would allow the instead ability.
Only cases where game rule dictates that a card goes to a player's control would cause one of them to be discarded (think convoluted examples like banding to your opponent's AutO and exchanging to your own judge in territory). Every other case, where a special ability would cause duplicates, cannot happen because those 'duplicates' are protected from being placed under that player's control.
